I like that this is a playful shot. I don't love the silhouette technique, as you can't really see the subjects well enough for my tastes. I think a photo of daddy swinging his daughter, or tossing her in the air, or dancing with her, would be lovely.
Swimming helps develop physical development because the kids are moving. Any movement is technically physical activity. Appropriate for ages because this is the perfect age to teach kids how to swim and once they're taught how to they won't want to stop.